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United States Patent |
6,149,790
|
Oikawa
,   et al.
|
November 21, 2000
|
Method of making iron-electroplated aluminum materials
Abstract
A method for making an aluminium material which is electroplated on its
aluminum or aluminium alloy base with iron or an iron alloy containing
2-20 weight % of chromium, and which can be utilized as a new structural
or functional material in various industrial fields. The material is
characterized in having an inter-diffusion layer produced between the base
and the plating and/or having such fine cracks produced in the plating
which can reserve well machine oil, work well for painting it, and be
impregnated with a resin for improving its wear resistance and so on.
Inventors:
|
Oikawa; Wataru (Nasugun, JP);
Takeuchi; Eiichi (Fujisawashi, JP)
|
Assignee:
|
Nippon Platec, K.K. ()
|
Appl. No.:
|
097030 |
Filed:
|
June 12, 1998 |
Foreign Application Priority Data
| Jul 04, 1997[JP] | 9-215396 |
| Jul 09, 1997[JP] | 9-218889 |
Current U.S. Class: |
205/113; 205/153; 205/196; 205/228; 205/255 |
Intern'l Class: |
C23C 028/00; C25D 005/50 |
Field of Search: |
205/50,113,139,153,196,213,227,228,255
|
References Cited
U.S. Patent Documents
1256954 | Feb., 1918 | Travers | 205/228.
|
4094749 | Jun., 1978 | Stange et al. | 205/113.
|
4221639 | Sep., 1980 | Ninagawa et al. | 428/624.
|
4388379 | Jun., 1983 | Klingenmaier | 428/613.
|
4655884 | Apr., 1987 | Hills | 205/181.
|
5368719 | Nov., 1994 | Troup-Packman | 205/213.
|
5516419 | May., 1996 | Phan et al. | 205/148.
|
Primary Examiner: Gorgos; Kathryn
Assistant Examiner: Leader; William T.
Attorney, Agent or Firm: Shlesinger Fitzsimmons Shlesinger
Claims
What is claimed is:
1. Method for making aluminum or aluminum alloy material electroplated with
an iron alloy containing 2-20 weight % of chromium, which comprises:
electroplating the material with the iron alloy containing 2-20 weight % of
chromium to form an electroplated surface with cracks then,
heat-treating the electroplated material at a temperature between about 450
and about 650.degree. C., producing an inter-diffusion layer at a boundary
area between a surface of the material and the iron alloy electroplated on
the surface, and
succeedingly cooling the electroplated material.
2. The method as claimed in claim 1, in which the cooling of the
electroplated material is conducted at a cooling speed of more than about
60.degree. C. per minute to effect growing of said cracks.
3. The method as claimed in claim 1, in which the cooling of the
electroplated material is conducted at a cooling speed of more than
5.degree. C. per minute and less than about 60.degree. C. per minute to
maintain the cracks as they are.
4. Method for making an aluminum or aluminum alloy material electroplated
with an iron alloy containing 2-20 weight % of chromium, which comprises;
electroplating the material with the iron alloy containing 2-20 weight % of
chromium to form an electroplated surface with cracks, and
applying to the electroplated surface a thermoplastic resin for coating
said surface of the material and impregnating the cracks therein.
5. Method for making an aluminum or aluminum alloy material electroplated
with an iron alloy containing 2-20 weight % of chromium, which comprises;
electroplating the material with the iron alloy containing 2-20 weight % of
chromium to form an electroplated surface with cracks, and
applying to and coating the electroplated surface with a thermosetting
resin mixed with lubricating solid particles for impregnating the cracks
in said surface.
Description
BACKGROUND OF THE INVENTION
This invention relates to a novel method of making iron-electroplated
aluminium or aluminium alloy materials, by which a selected or whole part
of surfaces of aluminium or aluminium alloy in the form of a sheet for
example is firmly electroplated by iron or iron alloy.
The materials made by this invention can widely be employed in various
industries including an automobile industry and electric appliance
industry. For example, in the automobile industry, there is every
indication that aluminium and aluminium alloys will be employed as much as
possible in order to lighten automobiles, while aluminium or aluminium
alloys as they are can hardly be structural materials for automobiles.
In this view, aluminium or aluminium alloys, surfaces of which are
iron-electroplated, have drawn our attention, because as they have
advantageous features such as good spot-weldability, they could be
structural materials for automobiles.
However, an iron layer which has been conventionally electroplated to
aluminium or aluminium alloy surfaces, peels off occasionally.
It is therefore an object of this invention to provide a method of making
iron-electroplated aluminium or aluminium alloy materials, plated iron
layer of which can hardly peel off from its aluminium or aluminium alloy
base, or can hardly cleave or fissure.
It is another object of this invention to provide a method of making
iron-electroplated aluminium or aluminium alloy materials, electroplated
iron layer of which can stand well against frictional and other wears.
Other objects of this invention will be apparent hereinunder from the
specification and from the recital of the appended claims.
SUMMARY OF THE INVENTION
In this invention, after surfaces of aluminium or an aluminium alloy were
electroplated by iron, they are subjected to a heat-treatment of a
temperature between about 450 and 650.degree. C., whereby an
inter-diffusion layer of Al and Fe is produced at the boundary area of the
aluminium or aluminium alloy base and the iron-electroplated layer on the
base. The inter-diffusion layer enhances the adhesion of the iron plating
with the aluminium base, and works to prevent the iron plating to peel off
from the aluminium base or to cleave or fissure. This is a characteristic
feature of this invention.
The aluminium or aluminium alloy material which has been heat-treated as
described above, has to be cooled. When the material is quenched rapidly
at a cooling speed of 60.degree. C./minute for example, fine cracks are
produced evenly all over the surfaces of iron plating. This is another
characteristic feature of this invention. Paints adhere very well to the
aluminium or aluminium alloy material having such cracks on its surfaces.
It will be noted in this connection that conventional zinc plated steel
sheets for automobiles are necessarily coated at their surfaces by zinc
phosphate films, so that paints can adhere well to them. The aluminium or
aluminium alloy material of this invention does not need such coating for
the sake of painting.
When the heat-treated material is gradually cooled, instead of being
rapidly quenched, at a cooling speed of 5-10.degree. C./minute for
example, cracks will not be produced on surfaces of the material,
resulting in providing the material with smooth electroplated surfaces.
This kind of material which is also within the scope of this invention,
can advantageously be employed in an electric appliance industry as light
weight magnetic shielding materials and so on.
The aluminium material made in accordance with this invention can be
lubricated well, since its electroplated and cracked surfaces can reserve
machine oil well, and can accordingly be excellent in wear resistance.
Iron plated and finely cracked surfaces of the aluminium material of this
invention may also be coated by thermoplastic resins such as PTFE and
nylon so that they can be excellent in anti-wear characteristics. When the
surfaces are dipped in a molten thermoplastic resin, a part of the resin
sinks into the surface cracks and solidifies in them at a room
temperature. As such resin which has sunk and solidified in the surface
cracks, works as roots of other part of the resin which has solidified
over the surfaces, the resin applied to the material can adhere as a whole
to the material firmly. When the iron electroplated aluminium material of
this invention thus coated with a thermoplastic resin is subjected to
sliding friction, for example, the resin becomes liquid by a frictional
heat and works as a lubricant.
Iron electroplated and cracked surfaces of the aluminium material of this
invention may also be coated by a thermosetting resin which has been
dissolved by an organic solvent and mixed with lubricating solid particles
of such fineness corresponding to or less than widths of the surface
cracks. The resin coat is heated, whereby the solvent is evaporated and
the thermosetting resin is solidified so that the lubricating particles
are fixed to the plated surfaces and cracks thereof by means of the
solidified resin. Particularly, those resin and lubricating particles
which have been adhered to the cracks, work as roots of the resin coating,
similarly to the above-mentioned thermoplastic resin coating.
Iron to be electroplated to aluminium or aluminium alloys in accordance
with this invention may be an iron alloy, especially the iron alloy viz.,
a steel containing Cr of 2-20 weight % and having a hardness of 800-1,200
HV. When this steel is electroplated to aluminium or aluminium alloy,
cracks are inevitably produced on plated surfaces. If desired to enlarge
the cracks, the iron plated material shall be quenched rapidly after
having it heat-treated in accordance with this invention, while if desired
to keep the cracks as they are, the plated material shall be gradually
cooled after the heat-treatment for producing an inter-diffusion layer
between the aluminium substrate and the plating.
THE DRAWINGS
FIG. 1 is a graph showing results, namely relative wear volumes under
various friction velocities, of sliding wear tests of the
iron-electroplated aluminium material obtained in accordance with this
invention in the following Example 3 and a comparative test material.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
EXAMPLE 1
After pretreatments (comprising degreasing, acidic activation, alkaline
etching, acidic activation, 1st substitution with zinc, dipping into
nitric acid, 2nd substitution with zinc, and so on, while water-washing
steps in the pretreatments being omitted), a rolled sheet of aluminium
alloy JIS 5052) of 2 mm in thickness was electroplated in 10 .mu.m in
thickness at its outer surfaces by iron under the following electroplating
conditions.
______________________________________
Compositions of plating bath:
______________________________________
ferrous chloride 300 g/l
ammonium chloride 20 g/l
Bath temperature: 50-55.degree. C.
Current density at cathode:
6A/dm.sup.2
Current efficiency at cathode:
95-100%
Electroplated iron films had a hardness of about 399 HV.
______________________________________
After water-washing and drying the aluminium alloy sheet thus electroplated
by iron, the sheet was heated at 570.degree. C. for five hours in an inert
atmosphere of N.sub.2 gas under a pressure of 2 bar, and quenched in a
similar atmosphere rapidly at a cooling speed of 60.degree. C./minute.
Tortoiseshell-like patterned fine cracks which were produced evenly almost
all over the iron plate, were observed by scanning with an electron
microscope.
The same aluminium sheet was iron-electroplated and heat-treated under the
same conditions, but was cooled gradually at a cooling speed of 5.degree.
C./minute. No crack was observed at the iron plate.
By the observation through an optical microscope and EPMA of the
above-described two kinds of iron-electroplated aluminium alloy materials
thus obtained, it was confirmed that inter-diffusion layers of Al and Fe
had been produced along boundary areas of the aluminium alloy base and
iron plate. It was also observed that they had adhered closely and firmly
to each other. They never cleaved even by 90.degree. bending test.
EXAMPLE 2
Rolled sheets of 2 mm in thickness of aluminium alloy JIS 5052) were
pretreated similarly to Example 1, and an iron alloy containing about 15
weight % of Cr was electroplated in thickness of 10 .mu.m on the outer
surfaces of sheets under the following conditions.
______________________________________
Bath compositions:
trichrome-plus made by Atotech Japan
Co. as a basic composition, added by
40 g/l of ferrous sulfate.
trichrome-plus having the compositions
correspondent to those for trivalent
chronium plating, and consisting of:
basic chromium sulfate (tanning agent)
120 g/l
ammonium formate 55 g/l
ammonium oxalate 10 g/l
potassium chloride 54 g/l
ammonium chloride 54 g/l
boric acid 40 g/l
Bath temperature:
30.degree. C.
Cathode: made of insoluble carbon
Current density:
15 A/dm.sup.2 for first 5 minutes, and
10 A/dm.sup.2 for succeeding 18 minutes
______________________________________
The iron-chromium alloy films electroplated on the sheets had a hardness of
about 800 HV. It was observed by an electron microscope that over the
films, there were produced tortoise-shell-like patterned fine cracks.
After water-washing and drying the sheets thus electroplated by the
iron-chromium alloy, they were heated to 570.degree. C. for 5 hours in an
inert atmosphere of N.sub.2 gas under a pressure of 2 bar, and
succeedingly quenched in the similar atmosphere rapidly at a cooling speed
of 60.degree. C./minute. It was observed that cracks on the plated
surfaces had grown further.
On the other hand, when the sheets were cooled gradually at a cooling speed
of 5.degree. C., the cracks on the plated surfaces did not change.
It was found by the observation through an optical micro-scope and EPMA of
vertically cut-out sectional structures of the above-described two kinds
of plated aluminium sheets that inter-diffusion layers had been produced
along boundary areas between the Al base and Fe plating, and that they had
adhered closely and firmly to each other. They were never cleaved or
fissured when subjected to 90.degree. bending tests.
EXAMPLE 3
To surface cracks of the aluminium alloy sheets of Example 2 which had been
electroplated by the Fe--Cr alloy but not been heat-treated, Nylon 11 was
impregnated under pressure, and the surfaces were coated by films of said
thermoplastic resin.
The sheets thus impregnated and coated by the resin were made as stationary
test pieces, while S45C of a sorbite structure (HQT) was made as rotary
test pieces. With these stationary and rotary test pieces, the sheets were
subjected to sliding wear tests, in which a pin-ring type wearing test
machine was employed, and their contact pressure was kept at 0.49 MPa.
The results are shown in FIG. 1 by a curve of THIS INVENTION MATERIAL.
For the sake of comparison, the same aluminium sheets of Example 2 were
electroplated by iron, and nitrided by a gas permeation process for
hardening the iron plating. After having been nitrided, this comparative
test sheets were gradually cooled at a cooling speed of 5.degree.
C./minute. As the sheets had no cracks on their plated surfaces, no
coating was applied on them.
The comparative test sheets were also subjected to the aforementioned
sliding wear tests, results of which are shown in FIG. 1 by a curve of THE
COMPARATIVE MATERIAL. Although the comparative material had a harder
plated surface than this invention material, the latter showed smaller
relative wear volumes than the former.
EXAMPLE 4
To surface cracks of the aluminium alloy sheets of Example 2 which had been
electroplated by the Fe--Cr alloy but not been heat-treated, an epoxy
resin, a thermosetting resin which had been dissolved by an organic
solvent and mixed well with lubricating MoS2 particles having a particle
size nearly equal to or less than widths of the cracks, was coated, and
then heated to about 150.degree. C. for evaporating the solvent and for
solidifying the resin.
The resin with the lubricating solid particles which sunk into the cracks
and solidified therein, became such roots which were in turn connected to
the resin coating and worked to prevent it to peel off from the plated
surface.
The aluminium material thus obtained in this Example showed a good wear
resistance which is comparable to this invention material of Example 3.
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